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Deep-Sea, Shrimp-like Creatures Survive by Eating Wood

A Hirondellea gigas specimen collected at a depth of 35,820 feet in the Mariana Trench's Challenger Deep.

Photograph courtesy JAMSTEC

Deep-sea, shrimp-like crustaceans get big by munching on sunken wood, even from shipwrecks, according to a new study of amphipods.

The specimens of Hirondellea gigas were collected in 2009 in the Mariana Trench's Challenger Deep, Earth's deepest point and the same location of National Geographic explorer and filmmaker James Cameron's record-breaking dive in March 2012.

During his dive, Cameron also saw H. gigas amphipods, which, at up to two inches (five centimeters) long, are huge among their kind—more than twice the size of their common beachside relatives, the sandhoppers.

H. gigas live in swarms at depths of or below 30,000 feet (10,000 meters), where very little food makes its way down from the surface. This had scientists stumped—how do the amphipods get the nutrition to become relatively giant?

Analysis of the Mariana Trench amphipods revealed the scavengers harbor powerful wood-busting enzymes that can digest "wood fall"—tree and plant debris swept into the ocean that occasionally sinks.

"They are relying on sunken leftovers as their food," study co-author Hideki Kobayashi, a marine biologist from the Japan Agency for Marine-Earth Science and Technology, said in an email.

Back in the lab, the research team identified the wood-digesting enzymes, which worked even better when the scientists re-created the high-pressure conditions of the deep ocean.

Similar digestive enzymes have been found in the guts of other plant-eating animals, such as termites. But unlike other deep-sea species, H. gigas does not seem to cultivate fungi or bacteria to aid its digestion.

"We think the amphipods make the enzymes themselves in their gut," said Kobayashi, whose study appeared August 15 in the journal PLoS ONE.